Efficient DRC profile transmission

ABSTRACT

A method (600) for decoding an encoded audio signal (102) is described. The encoded audio signal (102) comprises a sequence of frames. Furthermore, the encoded audio signal (102) is indicative of a plurality of different dynamic range control (DRC) profiles for a corresponding plurality of different rendering modes. Different subsets of DRC profiles from the plurality of DRC profiles are comprised within different frames of the sequence of frames, such that two or more frames of the sequence of frames jointly comprise the plurality of DRC profiles. The method (600) comprises determining a first rendering mode from the plurality of different rendering modes; determining (609, 610) one or more DRC profiles from a subset of DRC profiles comprised within a current frame of the sequence of frames; determining (611) whether at least one of the one or more DRC profiles is applicable to the first rendering mode; selecting (604) a default DRC profile as a current DRC profile, if none of the one or more DRC profiles is applicable to the first rendering mode; wherein definition data of the default DRC profile is known at a decoder (100) for decoding the encoded audio signal (102); and decoding the current frame using the current DRC profile.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation from U.S. patent application Ser. No.17/022,152 filed Sep. 16, 2020, which is a continuation from U.S. patentapplication Ser. No. 16/420,473 filed May 23, 2019, now U.S. Pat. No.10,783,897, which is a continuation from U.S. patent application Ser.No. 16/026,529 filed Jul. 3, 2018, now U.S. Pat. No. 10,354,670, whichis a continuation from U.S. patent application Ser. No. 15/513,546 filedMar. 22, 2017, now U.S. Pat. No. 10,020,001, which is the U.S. nationalstage of PCT International Application No. PCT/EP2015/072371 filed Sep.29, 2015, which claims the benefit of priority from U.S. ProvisionalPatent Application No. 62/058,228 filed Oct. 1, 2014, each of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present document relates to the processing of audio signals. Inparticular, the present document relates to a method and a correspondingsystem for transmitting Dynamic Range Control (DRC) profiles in abandwidth efficient manner.

BACKGROUND

The increasing popularity of media consumer devices has created newopportunities and challenges for the creators and distributors of mediacontent for playback on those devices, as well as for the designers andmanufacturers of the devices. Many consumer devices are capable ofplaying back a broad range of media content types and formats includingthose often associated with high-quality, wide bandwidth and widedynamic range audio content for HDTV, Blu-ray or DVD. Media processingdevices may be used to play back this type of audio content either ontheir own internal acoustic transducers or on external transducers suchas headphones or high quality home theater systems; however, all theseplayback systems and environment pose significantly differentrequirements on the dynamic range of the audio signal due to varyingnoise levels in the environment or due to the limited capability of theplayback system to reproduce the required sound pressure levels withoutdistortion. Limiting the dynamic range depending on the environment isan approach to provide high quality and intelligibility across a broadrange of different rendering devices having different renderingcapabilities and listening environments, i.e. across a broad range ofrendering modes.

The present document addresses the technical problem of providingcreators and distributors of media content with bandwidth efficientmeans for enabling the reproduction of audio signals at high quality andintelligibility on a broad range of different rendering devices havingdifferent rendering capabilities.

SUMMARY

According to an aspect a method for generating an encoded audio signalis described. The encoded audio signal comprises a sequence of frames.The encoded audio signal is indicative of a plurality of differentdynamic range control (DRC) profiles for a corresponding plurality ofdifferent rendering modes. The method comprises inserting differentsubsets of DRC profiles from the plurality of DRC profiles intodifferent frames of the sequence of frames, such that two or more framesof the sequence of frames jointly comprise the plurality of DRCprofiles.

According to a further aspect, a method for decoding an encoded audiosignal is described. The encoded audio signal comprises a sequence offrames. Furthermore, the encoded audio signal is indicative of aplurality of different dynamic range control (DRC) profiles for acorresponding plurality of different rendering modes. Different subsetsof DRC profiles from the plurality of DRC profiles are comprised withindifferent frames of the sequence of frames, such that two or more framesof the sequence of frames jointly comprise the plurality of DRCprofiles. The method comprises determining a first rendering mode fromthe plurality of different rendering modes, and determining one or moreDRC profiles from a subset of DRC profiles comprised within a currentframe of the sequence of frames. Furthermore, the method comprisesdetermining whether at least one of the one or more DRC profiles isapplicable to the first rendering mode. In addition, the methodcomprises selecting a default DRC profile as a current DRC profile, ifnone of the one or more DRC profiles is applicable to the firstrendering mode, wherein definition data of the default DRC profile isknown at a decoder for decoding the encoded audio signal. Furthermore,the method comprises decoding the current frame using the current DRCprofile.

According to a further aspect, a bitstream comprising an encoded audiosignal is described. The encoded audio signal comprises a sequence offrames. The encoded audio signal is indicative of a plurality ofdifferent dynamic range control (DRC) profiles for a correspondingplurality of different rendering modes. The different subsets of DRCprofiles from the plurality of DRC profiles are comprised withindifferent frames of the sequence of frames, such that two or more framesof the sequence of frames jointly comprise the plurality of DRCprofiles.

According to another aspect, an encoder for generating an encoded audiosignal is described. The encoded audio signal comprises a sequence offrames. The encoded audio signal is indicative of a plurality ofdifferent dynamic range control (DRC) profiles for a correspondingplurality of different rendering modes. The encoder is configured toinsert different subsets of DRC profiles from the plurality of DRCprofiles into different frames of the sequence of frames, such that twoor more frames of the sequence of frames jointly comprise the pluralityof DRC profiles.

According to a further aspect, a decoder for decoding an encoded audiosignal is described. The encoded audio signal comprises a sequence offrames. The encoded audio signal is indicative of a plurality ofdifferent dynamic range control (DRC) profiles for a correspondingplurality of different rendering modes. The different subsets of DRCprofiles from the plurality of DRC profiles are comprised withindifferent frames of the sequence of frames, such that two or more framesof the sequence of frames jointly comprise the plurality of DRCprofiles. The decoder is configured to determine a first rendering modefrom the plurality of different rendering modes, to determine one ormore DRC profiles from a subset of DRC profiles comprised within acurrent frame of the sequence of frames, to determine whether at leastone of the one or more DRC profiles is applicable to the first renderingmode, to select a default DRC profile as a current DRC profile, if noneof the one or more DRC profiles is applicable to the first renderingmode; wherein definition data of the default DRC profile is known at thedecoder; and to decode the current frame using the current DRC profile.

According to a further aspect, a software program is described. Thesoftware program may be adapted for execution on a processor and forperforming the method steps outlined in the present document whencarried out on the processor.

According to another aspect, a storage medium is described. The storagemedium may comprise a software program adapted for execution on aprocessor and for performing the method steps outlined in the presentdocument when carried out on the processor.

According to a further aspect, a computer program product is described.The computer program may comprise executable instructions for performingthe method steps outlined in the present document when executed on acomputer.

It should be noted that the methods and systems including its preferredembodiments as outlined in the present patent application may be usedstand-alone or in combination with the other methods and systemsdisclosed in this document. Furthermore, all aspects of the methods andsystems outlined in the present patent application may be arbitrarilycombined. In particular, the features of the claims may be combined withone another in an arbitrary manner.

SHORT DESCRIPTION OF THE FIGURES

The invention is explained below in an exemplary manner with referenceto the accompanying drawings, wherein

FIG. 1 and FIG. 2 illustrate an example audio decoder and an exampleaudio encoder, respectively;

FIG. 3 and FIG. 4 illustrate example dynamic range compression curves;

FIG. 5 illustrates an example sequence of frames; and

FIG. 6 , consisting of FIG. 6A and FIG. 6B, shows a flow chart of anexample method for selecting a DRC profile.

DETAILED DESCRIPTION

As indicated above, the present document addresses the technical problemof enabling a designer and/or distributor of audio content to controlthe quality and intelligibility of the audio content for different typesof rendering modes. An example rendering mode is a home theatrerendering mode, where audio content is played back using transducerswhich typically allow for a very wide dynamic range in a quietenvironment. Another example rendering mode is a flat-panel mode, wherethe audio content is played back using transducers of e.g. a TV set,which typically allow for a reduced dynamic range compared to a hometheatre. A further example rendering mode is a portable speaker mode,where the audio content is played back using the loudspeakers of aportable electronic device (such as a smartphone). The dynamic range ofthis rendering mode is typically small compared to the above mentionedrendering modes and often the environment is noisy. Another examplerendering mode is a portable headphone mode, where the audio content isplayed back using headphones in conjunction with a portable electronicdevice. The dynamic range is limited but typically higher than thedynamic range which is provided by the loudspeakers of the portableelectronic device.

In order to allow for a high quality and high intelligibility for thedifferent rendering modes, different DRC (Dynamic Range Control)profiles for the different rendering modes may be provided along withthe audio content. The audio content may be transmitted in a sequence offrames. The sequence of frames may comprise I (i.e. independent) frameswhich may be decoded independently from previous or succeeding frames.Furthermore, the sequence of frames may comprise other types of frames(e.g. P and/or B frames) which typically exhibit a dependency withregards to a previous and/or a succeeding frame. At least some of theframes of the sequence of frames may comprise a plurality of differentDRC profiles for a plurality of different rendering modes. Inparticular, the I-frames of the sequence of frames may comprise theplurality of DRC profiles.

By inserting a plurality of different DRC profiles into a sequence ofaudio frames, an audio decoder is enabled to select an appropriate DRCprofile for a particular rendering mode. As a result, it may be ensuredthat the rendered audio signal has a high quality (notably no clippingor distortion introduced by the transducers) and a high intelligibility.

In the following, various aspects of dynamic range control aredescribed. Without customized dynamic range control, input audioinformation (e.g., PCM samples, time-frequency samples in a QMF matrix,etc.) is often reproduced at a playback device at loudness levels thatare inappropriate for the playback device's specific playbackenvironment (that is, including the device's physical and/or mechanicalplayback limitations), as the playback device's specific playbackenvironment might be different from a target playback environment forwhich the encoded audio content had been coded at an encoding device.

Techniques as described herein can be used to support dynamic rangecontrol of a wide variety of audio content customized to any of a widevariety of playback environments while maintaining perceptual qualitiesof the audio content and while maintaining an artist's intent ofadapting the content to different listening environments.

Dynamic Range Control (DRC) refers to time-variant, level-dependentaudio processing operations that alter (e.g., compress, cut, expand,boost, etc.) the signal in order to convert an input dynamic range ofloudness levels in audio content into an output dynamic range that isdifferent from the input dynamic range. For example, in a dynamic rangecontrol scenario, soft sounds may be mapped (e.g., boosted, etc.) tohigher loudness levels and loud sounds may be mapped (e.g., cut, etc.)to lower loudness values. As a result, in a loudness domain, an outputrange of loudness levels becomes smaller than the input range ofloudness levels in this example. In some embodiments, the dynamic rangecontrol, however, may be reversible so that the original range isrestored. For example, an expansion operation may be performed torecover the original range so long as mapped loudness levels in theoutput dynamic range, as mapped from original loudness levels, are at orbelow a clipping level, each unique original loudness level is mapped toa unique output loudness level, etc.

DRC techniques as described herein can be used to provide a betterlistening experience in certain playback environments or situations. Forexample, soft sounds in a noisy environment may be masked by the noisethat renders the soft sounds inaudible. Conversely, loud sounds may notbe desired in some situations, for example, bothering neighbors (e.g.within a “late-night” listening mode). Many devices, typically withsmall form-factor loudspeakers, cannot reproduce sound at high outputlevels or cannot reproduce sound without perceptible distortion. In somecases the lower signal levels may be reproduced below the human hearingthreshold. The DRC techniques may perform mapping of input loudnesslevels to output loudness levels based on DRC gains (e.g., scalingfactors that scale audio amplitudes, boost ratios, cut ratios, etc.)looked up with a dynamic range compression curve.

A dynamic range compression curve refers to a function (e.g., a lookuptable, a curve, a multi-segment piecewise lines, etc.) that mapsindividual input loudness levels (e.g., of sounds other than dialogues,etc.) as determined from individual audio data frames to correspondingoutput loudness levels, and by consequence to individual gains or gainsfor dynamic range control in order to translate the input loudnesslevels to the corresponding output loudness levels. Each of theindividual gains indicates an amount of gain to be applied to the signalto map a corresponding individual input loudness level to the intendedoutput loudness level. Output loudness levels after applying theindividual gains represent target loudness levels for audio content inthe individual audio data frames in a specific playback environment.

In addition to specifying mappings between gains and loudness levels, adynamic range compression curve may include, or may be provided with,specific release times and attack times in applying specific gains. Anattack refers to an increase of signal energy (or loudness) betweensuccessive time samples, whereas a release refers to a decrease ofenergy (or loudness) between successive time samples. An attack time(e.g., 10 milliseconds, 20 milliseconds, etc.) refers to a time constantused in smoothing DRC gains when the corresponding signal is in attackmode. A release time (e.g., 80 milliseconds, 100 milliseconds, etc.)refers to a time constant used in smoothing DRC gains when thecorresponding signal is in release mode. In some embodiments,additionally, optionally or alternatively, the time constants are usedfor smoothing of the signal energy (or loudness) prior to determiningthe DRC gain.

Different dynamic range compression curves may correspond to differentplayback environments (i.e. to different rendering modes). For example,a dynamic range compression curve for a playback environment of a flatpanel TV may be different from a dynamic range compression curve for aplayback environment of a portable device. A playback device may havetwo or more playback environments. For example, a first dynamic rangecompression curve for a first playback environment of a portable devicewith speakers may be different from a second dynamic range compressioncurve for a second playback environment of the same portable device withheadset.

FIG. 1 shows a block diagram of example components of an audio decoder100. The audio decoder 100 comprises a data extractor 104, a dynamicrange controller 106, and an audio renderer 108. The data extractor 104is configured to receive an encoded input signal 102. An encoded inputsignal 102 as described herein may be a bitstream that contains encoded(e.g., compressed, etc.) input audio data frames (notably a sequence ofaudio frames) and possibly metadata. The bitstream may be an AC-4bitstream. The data extractor 104 is configured to extract/decode inputaudio data frames and metadata from the encoded input signal 102. Eachof the input audio data frames comprises a plurality of coded audio datablocks each of which represents a plurality of audio samples. Each framerepresents a (e.g., constant) time interval comprising a certain numberof audio samples. The frame size may vary with the sample rate and codeddata rate. The audio samples are quantized audio data elements (e.g.,input PCM samples, input time-frequency samples in a QMF matrix, etc.)representing spectral content in one, two or more (audio) frequencybands or frequency ranges. The quantized audio data elements in theinput audio data frames may represent sound pressure waves in a digital(quantized) domain. The quantized audio data elements may cover a finiterange of loudness levels at or below a largest possible value (e.g., aclipping level, a maximum loudness level, etc.).

The metadata can be used by the audio decoder 100 to process the inputaudio data frames. The metadata may include a variety of operationalparameters relating to one or more operations to be performed by thedecoder 100, one or more dynamic range compression curves (i.e. one ormore DRC profiles), normalization parameters relating to dialogueloudness levels represented in the input audio data frames, etc. Adialogue loudness level may refer to a (e.g., psychoacoustic,perceptual, etc.) level of dialogue loudness, program loudness, averagedialogue loudness, etc., in an entire program (e.g., a movie, a TVprogram, a radio broadcast, etc.), a portion of a program, a dialogue ofa program, etc.

The operation and functions of the decoder 100, or some or all of themodules (e.g., the data extractor 104, the dynamic range controller 106,etc.), may be adapted in response to the metadata extracted from theencoded input signal 102. For example, the metadata—including but notlimited to dynamic range compression curves, dialogue loudness levels,etc.—may be used by the decoder 100 to generate output audio dataelements (e.g., output PCM samples, output time-frequency samples in aQMF matrix, etc.) in the digital domain. The output data elements canthen be used to drive audio channels or speakers to achieve a specifiedloudness or reference reproduction level during playback in a specificplayback environment.

The dynamic range controller 106 may be configured to receive some orall of the audio data elements in the input audio data frames and themetadata, perform audio processing operations (e.g., dynamic rangecontrol operations, gain smoothing operations, gain limiting operations,etc.) on the audio data elements in the input audio data frames based atleast in part on the metadata extracted from the encoded audio signal102, etc.

In particular, the dynamic range controller 106 may comprise a selector110, a loudness calculator 112 and/or DRC gain unit 114. The selector110 may be configured to determine a speaker configuration (e.g., hometheatre mode, flat panel mode, portable device with speakers mode,portable device with headphones mode, a 5.1 speaker configuration mode,a 7.1 speaker configuration mode, etc.) relating to a specific playbackenvironment at the decoder 100. The speaker configuration may also bereferred to as the rendering mode. Furthermore, the selector 110 may beconfigured to select a specific dynamic range compression curve (i.e. aDRC profile) from the dynamic range compression curves (i.e. from theplurality of DRC profiles) extracted from the metadata of the encodedinput signal 102.

The loudness calculator 112 may be configured to calculate one or moretypes of loudness levels as represented by the audio data elements inthe input audio data frames. Examples of types of loudness levelsinclude, but are not limited to: any of individual loudness levels overindividual frequency bands in individual channels over individual timeintervals, broadband (or wideband) loudness levels over a broad (orwide) frequency range in individual channels, loudness levels asdetermined from or smoothed over an audio data block or frame, loudnesslevels as determined from or smoothed over more than one audio datablock or frame, loudness levels smoothed over one or more timeintervals, etc. Zero, one or more of these loudness levels may bealtered for the purpose of dynamic range control by the decoder 100.

To determine the loudness levels, the loudness calculator 112 candetermine one or more time-dependent physical sound wave properties suchas spatial and/or local pressure levels at specific audio frequencies,etc., as represented by the audio data elements in the input audio dataframes. The loudness calculator 112 can use the one or more time-varyingphysical wave properties to derive one or more types of loudness levelsbased on one or more psychoacoustic functions modeling human loudnessperception. A psychoacoustic function may be a non-linear function—asconstructed based on a model of the human auditory system—thatconverts/maps specific spatial pressure levels at specific audiofrequencies to specific loudness for the specific audio frequencies.

A (e.g., broadband, wideband, etc.) loudness level over multiple (audio)frequencies or multiple frequency bands may be derived throughintegration of specific loudness levels over the multiple (audio)frequencies or multiple frequency bands. Time-averaged, smoothed, etc.,loudness levels over one or more time intervals (e.g., longer than thatrepresented by audio data elements in an audio data block or frame,etc.) may be obtained by using one or more smoothing filters that areimplemented as a part of the audio processing operations in the decoder100. Another example method for determining a (broadband) loudness levelis specified in ITU-R BS.1770. The method which is specified in ITU-RBS.1770 applies time domain filtering on a time domain input audiosignal and then calculates an RMS (root mean square) level on eachchannel of the input audio signal before integrating over the channelsand gating the resulting loudness level.

A specific loudness level for different frequency bands may becalculated per audio data block of certain (e.g., 256, etc.) samples.Pre-filters may be used to apply frequency weighting (e.g., similar toIEC B-weighting, etc.) to the specific loudness levels in integratingthe specific loudness levels into a broadband (or wideband) loudnesslevel. A summation of broad loudness levels over two or more channels(e.g., left front, right front, center, left surround, right surround,etc.) may be performed to provide an overall loudness level of the twoor more channels.

An overall loudness level may refer to a broadband (wideband) loudnesslevel in a single channel (e.g., center, etc.) of a speakerconfiguration. An overall loudness level may refer to a broadband (orwideband) loudness level in a plurality of channels. The plurality ofchannels may be all channels in a speaker configuration (i.e. for arendering mode). Additionally, optionally or alternatively, theplurality of channels may comprise a subset of channels (e.g., a subsetof channels comprising left front, right front, and low frequency effect(LFE); a subset of channels comprising left surround and right surround;a subset of channels comprising center; etc.) in a speakerconfiguration.

A (e.g., broadband, wideband, overall, specific, etc.) loudness levelmay be used as input to look up a corresponding (e.g., static,pre-smoothing, pre-limiting, etc.) DRC gain from the selected dynamicrange compression curve. The loudness level to be used as input to lookup the DRC gain may be first adjusted or normalized with respect to adialogue loudness level from the metadata extracted from the encodedaudio signal 102 and/or with respect to an output reference level of therendering mode. The adjustments and normalization related to adjustingthe dialogue loudness level/output reference level may be performed on aportion of the audio content in the encoded audio signal 102 in anon-loudness domain (e.g., a SPL domain, etc.), before specific spatialpressure levels represented in the portion of the audio content in theencoded audio signal 102 are converted or mapped to specific loudnesslevels of the portion of the audio content in the encoded audio signal102.

The DRC gain unit 114 may be configured with a DRC algorithm to generategains (e.g., for dynamic range control, for gain limiting, for gainsmoothing, etc.) and to apply the gains to one or more loudness levelsin the one or more types of loudness levels represented by the audiodata elements in the input audio data frames to achieve target loudnesslevels for the specific playback environment. The application of gainsas described herein (e.g., DRC gains, etc.) may happen in the loudnessdomain. By way of example, gains may be generated based on the loudnesscalculation (which may be in Sone or just the SPL value compensated forthe dialog loudness level, for example, with no conversion), smoothedand applied directly to the input signal. Techniques as described hereinmay apply the gains to a signal in the loudness domain, and then convertthe signal from the loudness domain back to the (linear) SPL domain andcalculate corresponding gains that are to be applied to the signal byassessing the signal before and after the gain was applied to the signalin the loudness domain. The ratio (or difference when represented in alogarithmic dB representation) then determines the corresponding gainfor the signal.

The DRC algorithm may operate with a plurality of DRC parameters. TheDRC parameters include the dialogue loudness level that has already beencomputed and embedded into the encoded audio signal 102 by an upstreamencoder 150 (as described in the context of FIG. 2 ) and can be obtainedfrom the metadata in the encoded audio signal 102 by the decoder 100.The dialogue loudness level from the upstream encoder 150 indicates anaverage dialogue loudness level (e.g., per program, relative to theenergy of a full-scale 1 kHz sine wave, relative to the energy of areference rectangular wave, etc.). The dialogue loudness level extractedfrom the encoded audio signal 102 may be used to reduce inter-programloudness level differences. The reference dialogue loudness level may beset to the same value between different programs in the same specificplayback environment at the decoder 100. Based on the dialogue loudnesslevel from the metadata, the DRC gain unit 114 can apply a dialogueloudness related gain to each audio data block in a program such that anoutput dialogue loudness level (or output reference level) averaged overa plurality of audio data blocks of the program is raised/lowered to a(e.g., pre-configured, system default, user-configurable, profiledependent, etc.) reference dialogue loudness level for the program. Thedialogue loudness level may also be used to calibrate the DRC algorithm,notably the null-band of the DRC algorithm may be adjusted to thedialogue loudness level. Alternatively, the desired output referencelevel may be used to calibrate the DRC algorithm when the DRC algorithmis applied to a signal to which a gain has been applied to change thedialogue loudness level to be equal to the desired output referencelevel. The dialog loudness level may correspond to a so called dialnormparameter, if speech gating has been applied to determine the dialnormparameter. In some embodiments, the dialog loudness level corresponds toa dialnorm parameter that is not determined by using speech gating, butby a gating based on a loudness level threshold.

The DRC gains may be used to address intra-program loudness leveldifferences by boosting or cutting signal portions in soft and/or loudsounds in accordance with the selected dynamic range compression curve.One or more of these DRC gains may be computed/determined by the DRCalgorithm based on the selected dynamic range compression curve and(e.g., broadband, wideband, overall, specific, etc.) loudness levels asdetermined from one or more of the corresponding audio data blocks,audio data frames, etc.

Loudness levels used to determine (e.g., static, pre-smoothing, pre-gainlimiting, etc.) DRC gains by looking up the selected dynamic rangecompression curve may be calculated on short intervals (e.g.,approximately 5.3 milliseconds, etc.). The integration time of the humanauditory system (e.g., approximately 200 milliseconds, etc.) may be muchlonger. The DRC gains obtained from the selected dynamic rangecompression curve may be smoothed with a time constant to take intoaccount the long integration time of the human auditory system. Toeffectuate fast rates of changes (increases or decreases) in loudnesslevels, short time constants may be used to cause changes in loudnesslevels in short time intervals corresponding to the short timeconstants. Conversely, to effectuate slow rates of changes (increases ordecreases) in loudness levels, long time constants may be used tochanges in loudness levels in long time intervals corresponding to thelong time constants.

The human auditory system may react to increasing loudness levels anddecreasing loudness levels with different integration time. Differenttime constants may be used for smoothing the static DRC gains looked upfrom the selected dynamic range compression curves, depending on whetherthe loudness level will be increasing or decreasing. For example, incorrespondence with the characteristics of the human auditory system,attacks (loudness level increasing) may be smoothed with relativelyshort time constants (e.g., attack times, etc.), whereas releases(loudness level decreasing) may be smoothed with relatively long timeconstants (e.g., release time, etc.).

A DRC gain for a portion (e.g., one or more of audio data blocks, audiodata frames, etc.) of audio content may be calculated using a loudnesslevel determined from the portion of audio content. The loudness levelto be used for looking up in the selected dynamic range compressioncurve may be first adjusted with respect to (e.g., in relation to, etc.)a dialogue loudness level (e.g., in a program of which the audio contentis a part, etc.) in the metadata extracted from the encoded audio signal102.

A reference dialogue loudness level/output reference level (e.g., −31dB_(FS) in the “Line” mode, −20 dB_(FS) in the “RF” mode, etc.) may bespecified or established for the specific playback environment at thedecoder 100. Additionally, alternatively or optionally, in someembodiments, users may be given control over setting or changing thereference dialogue loudness level at the decoder 100.

The DRC gain unit 114 may be configured to determine a dialogue loudnessrelated gain to the audio content to cause a change from the inputdialogue loudness level to the reference dialogue loudness level as theoutput dialogue loudness level.

The audio renderer 108 may be configured to generate (e.g.,multi-channel, etc.) channel-specific audio data 116 for the specificspeaker configuration after applying gains as determined based on DRC,gain limiting, gain smoothing, etc., to the input audio data extractedfrom the encoded audio signal 102. The channel-specific audio data 116may be used to drive speakers, headphones, etc., represented in thespeaker configuration.

Additionally and/or optionally, the decoder 100 may be configured toperform one or more other operations relating to processing, rendering,downmixing, resampling etc., relating to the input audio data.

Techniques as described herein can be used with a variety of speakerconfigurations corresponding to a variety of different surround soundconfigurations (e.g., 2.0, 3.0, 4.0, 4.1, 4.1, 5.1, 6.1, 7.1, 7.2, 10.2,a 10-60 speaker configuration, a 60+ speaker configuration, objectsignals or combinations of object signals, etc.) and a variety ofdifferent rendering environment configurations (e.g., cinema, park,opera houses, concert halls, bars, homes, auditoriums, etc.).

FIG. 2 illustrates an example encoder 150. The encoder 150 may comprisean audio content interface 152, a dialogue loudness analyzer 154, a DRCreference repository 156 and an audio signal encoder 158. The encoder150 may be a part of a broadcast system, an internet-based contentserver, an over-the-air network operator system, a movie productionsystem, etc.

The audio content interface 152 may be configured to receive audiocontent 160 and audio content control input 162 for generating anencoded audio signal 102 based at least on some or all of the audiocontent 160 and the audio content control input 162. For example, theaudio content interface 152 may be used to receive the audio content 160and the audio content control input 162 from a content creator, acontent provider, etc.

The audio content 160 may constitute some or all of overall media datathat comprises audio only, audiovisual, etc. The audio content 160 maycomprise one or more of portions of a program, a program, severalprograms, one or more commercials, etc.

The dialogue loudness analyzer 154 may be configured todetermine/establish one or more dialogue loudness levels of one or moreportions (e.g., one or more programs, one or more commercials, etc.) ofthe audio content 152. The audio content may be represented by one ormore sets of audio tracks. Dialogue audio content of the audio contentmay be in separate audio tracks and/or at least a portion of dialogueaudio content of the audio content may be in audio tracks comprisingnon-dialogue audio content.

The audio content control input 162 may comprise some or all of usercontrol input, control input provided by a system/device external to theencoder 150, control input from a content creator, control input from acontent provider, etc. For example, a user such as a mixing engineer,etc., can provide/specify one or more dynamic range compression curveidentifiers; the identifiers may be used to retrieve one or more dynamicrange compression curves that fit the audio content 160 best from a datarepository such as a DRC reference repository (156), etc.

The DRC reference repository 156 may be configured to store DRCreference parameter sets, etc. The DRC reference parameter sets mayinclude definition data for one or more dynamic range compressioncurves, etc. The encoder 150 may (e.g., concurrently) encode more thanone dynamic range compression curve into the encoded audio signal 102.Zero, one, or more of the dynamic range compression curves may bestandard-based, proprietary, customized, decoder-modifiable, etc. By wayof example, the dynamic range compression curves of FIG. 3 and FIG. 4may be (e.g., concurrently) encoded into the encoded audio signal 102.

The audio signal encoder 158 may be configured to receive the audiocontent from the audio content interface 152, the dialogue loudnesslevels from the dialogue loudness analyzer 154, retrieve one or more DRCreference parameter sets (i.e. DRC profiles) from the DRC referencerepository 156, format audio content into audio data blocks/frames,format the dialogue loudness levels, the DRC reference parameter sets,etc., into metadata (e.g., metadata containers, metadata fields,metadata structures, etc.) and encode the audio data blocks/frames andthe metadata into the encoded audio signal 102.

Audio content to be encoded into an encoded audio signal 102 asdescribed herein may be received in one or more of a variety of sourceaudio formats in one or more of a variety of ways, such as wirelessly,via a wired connection, through a file, via an internet download, etc.An encoded audio signal 102 as described herein can be a part of anoverall media data bitstream (e.g., for an audio broadcast, an audioprogram, an audiovisual program, an audiovisual broadcast, etc.). Themedia data bitstream can be accessed from a server, a computer, a mediastorage device, a media database, a media file, etc. The media databitstream may be broadcasted, transmitted or received through one ormore wireless or wired network links. A media data bitstream may also becommunicated through an intermediary such as one or more of networkconnections, USB connections, wide area networks, local area networks,wireless connections, optical connections, buses, crossbar connections,serial connections, etc.

Any of the components depicted (e.g., FIG. 1 , FIG. 2 ) may beimplemented as one or more processes and/or one or more IC circuits(e.g., ASICs, FPGAs, etc.), in hardware, software, or a combination ofhardware and software.

FIG. 3 and FIG. 4 illustrate example dynamic range compression curvesthat can be used by the DRC gain unit 104 in the decoder 100 to derivethe DRC gains from input loudness levels. As illustrated, a dynamicrange compression curve may be centered around a reference loudnesslevel (e.g. the output reference level) in a program in order to provideoverall gains that are appropriate for the specific playbackenvironment. Example definition data (e.g., in the metadata of theencoded audio signal 102) of the dynamic range compression curve (e.g.,including but not limited to any of: boost ratios, cut ratios, attacktimes, release times, etc.) are shown in the following table. Thedifferent profiles (e.g., film standard, film light, music standard,music light, speech, etc.) may be different for different playbackenvironments (e.g., at the decoder 100):

TABLE 1 Profile Parameter Film standard Film light Music Standard Musiclight Speech Time Constant Selection Attack Threshold (dB) 15 15 15 1510 Release Threshold (dB) 20 20 20 20 10 Fast Attack Time Constant (ms)10 10 10 10 10 Slow Attack Time Constant (ms) 100 100 100 100 100 SlowRelease Time Constant (ms) 3000 3000 10000 3000 1000 Fast Release TimeConstant (ms) 1000 1000 1000 1000 200 Holdoff period (ms) 53 53 53 53 53Compression Curve Maximum Boost (dB) 6 6 12 12 15 Maximum Boost Range(<=dB) −43 −53 −55 −65 −50 Boost Ratio 2:1 2:1 2:1 2:1 19:15 Boost Range(dB) [−43, . . . , −31] [−53, . . . , −41] [−55, . . . , −31] [−65, . .. , −41] [−50, . . . , −31] Null Band Width (dB) 5 20 5 20 5 Null BandRange (dB) [−31, . . . , −26] [−41, . . . , −21] [−31, . . . , −26][−41, . . . , −21] [−31, . . . , −26] Cut Ratio 2:1 2:1 2:1 2:1 2:1 CutRatio Range (dB) [−26, . . . , −16] [−21, . . . , −11] [−26, . . . ,−16] [−21, . . . , 27]  [−26, . . . , −16] Secondary Cut Ratio 20:1920:19 20:19 20:19 Secondary Cut Ratio Range (dB) [−16, . . . , 4]  [−11,. . . , 9]  [−16, . . . , 4]  [−16, . . . , 4]  Maximum Cut (dB) −24 −24−24 −24 −24 Maximum Cut Range (>=dB) 4 9 4 27 4

One or more compression curves described in terms of loudness levels indB_(SPL) or dB_(FS) and gains in dB relating to dB_(SPL) may bereceived, whereas DRC gain calculation is performed in a differentloudness representation that has a non-linear relation with dB_(SPL)loudness levels (e.g. Sone). The compression curve used in the DRC gaincalculation may then be converted to be described in terms of thedifferent loudness representation (e.g. Sone).

FIG. 5 illustrates an example encoded audio signal 102 which comprises asequence of frames (numbered as n+1 up to n+30, with n being aninteger). In the illustrated example, every 5th frame is an I-frame. Inthe illustrated example, the I-frame (n+1) comprises a plurality of DRCprofiles (identified as AVR (Audio/Video Receiver) for a home theatre,Flat-panel, Portable HP (headphone) and Portable SP (speakers)). EachDRC profile comprises a dynamic range compression curve as shown inFIGS. 3 and 4 .

The plurality of DRC profiles may be inserted repeatedly within theI-frames of the sequence of frames. This allows a decoder 100 todetermine the appropriate DRC profile for the encoded audio signal 102and for a current rendering mode upon startup of the encoded audiosignal 102, upon tune-in into a running audio program and/or subsequentto a splicing point. On the other hand, the repeated transmission of acomplete set of DRC profiles leads to a relatively high bitstreamoverhead. In view of this, it is proposed to transmit changing subsetsof DRC profiles within the I-frames of the encoded audio signal 102.

FIG. 5 illustrates an example for inserting DRC profiles within asequence of frames. In the illustrated example, only a single DRCprofile from the complete set of DRC profiles is inserted into anI-frame. The DRC profile which is inserted into an I-frame changes fromI-frame to I-frame, and by consequence, subsequent to N I-frames (withN=4 in the illustrated example), the decoder 100 has received thecomplete set of N DRC profiles. By doing this, the data rate fortransmitting the complete set of DRC profiles can be reduced, while atthe same time ensuring that the decoder 100 receives the complete set ofDRC profiles within a reasonable amount of time.

FIG. 6A and FIG. 6B show a flow chart of an example method 600 fordetermining a DRC profile for decoding a frame of an encoded audiosignal 102. The method 600 may be executed by the decoder 100 (notablyby the selector 110). Upon start of reception of the encoded audiosignal 102, the DRC profile which is used by the decoder 100 may beinitialized. The DRC profile which is used for decoding a current frameof the encoded audio signal 102 may be referred to as the current DRCprofile. As such, upon startup, the current DRC profile may beinitialized. In particular, a default DRC profile (which is available atthe decoder 100) may be set to be the current DRC profile which is usedfor rending the current frame (method step 601). Hence, a variable“profile” may be set to a default DRC profile (profile=Default DRCProfile). Furthermore, the decoder 100 may track a previously usedprofile. The previously used profile may be set to undefined(prev_profile=undefined).

The method 600 may further comprise the step 602 of fetching a new framewhich is to be decoded (i.e. the current frame) from the encoded audiosignal 102. In step 603, it is verified, whether the new frame is anI-frame which might comprise a DRC profile. If the new frame is not anI-frame, then the method 600 proceeds with step 604 and processes thenew frame using the current DRC profile. Furthermore, the previouslyused profile is set to the current DRC profile in method step 605(prev_profile=profile).

If the new frame is an I-frame then it may be checked in method step606, whether the I-frame comprises DRC data. By way of example, themetadata of the I-frame may comprise a flag which is indicative ofwhether the I-frame comprises DRC data. If no DRC data is present, thenthe method 300 may proceed with steps 604, 605. Otherwise, the methodmay proceed with method step 607.

In method step 607 it may be verified, whether the new frame is thefirst frame of the encoded audio signal 102 which is to be decoded. Ascan be seen from the flow chart of FIG. 6A and FIG. 6B, this may beverified by checking the prev_profile variable. If the prev_profilevariable is undefined, then the new frame is the first frame to bedecoded. If the new frame is the first frame to be decoded, then thedecoder 100 may use a predefined DRC profile other than the default DRCprofile. For this purpose, the metadata of the new frame may comprise anidentifier (ID) for such a predefined DRC profile. Such a predefined DRCprofile may be stored within a database at the decoder 100. The use of apredefined DRC profile may provide a bitrate efficient means forsignaling a to-be-used DRC profile to the decoder 100, because only theID of the predefined profile needs to be transmitted (method step 608).Predefined DRC profiles which are signaled using an ID may also bereferred to as implicit DRC profiles.

It should be noted that in some cases, it may be beneficial to only usea single predefined DRC profile other than the default DRC profile. Insuch a case, the decoder 100 may be configured to set the profilevariable to the predefined (i.e. implicit) DRC profile, withoutreceiving any ID within the metadata of the new frame.

The method 600 may further comprise verifying whether the metadata ofthe new frame comprises one or more explicit DRC profiles (step 609). Anexplicit DRC profile may comprise an ID for identifying the explicit DRCprofile. Furthermore, the explicit DRC profile typically comprisesdefinition data for a dynamic range compression curve as illustrated inFIGS. 3 and 4 . The dynamic range compression curve may be defined as apiecewise linear function. Furthermore, the explicit DRC profile mayindicate a range of output reference levels (ORL) for which the explicitDRC profile is applicable. By way of example, the default DRC profileand/or the predefined (implicit) DRC profile may be applicable foroutput reference levels which range from −31 dB FS up to 0 dB FS.

The ORL of a rendering device may indicate the dynamic rangecapabilities of the rendering device. Typically the dynamic rangecapabilities decrease with increasing ORL. In case of a high ORL,compression curves with a high degree of compression should be used, inorder to render an audio signal in an intelligible manner withoutclipping. On the other hand, in case of a low ORL, compression may bereduced to render audio signals with a high dynamic range. Due to thehigh dynamic range capabilities of the rendering device, intelligibilityof the audio signal is nevertheless ensured.

If the metadata of the new frame comprises at least one explicit DRCprofile, the profile data of a first DRC profile is read (step 610).Furthermore, it is verified whether the range of ORL of the first DRCprofile is applicable to the currently used rendering device (step 611).If this is not the case, then the method 600 proceeds to look foranother explicit DRC profile within the metadata of the new frame. Onthe other hand, if an explicit DRC profile is applicable to therendering device, then this explicit DRC profile may be set to be thecurrent DRC profile, which is to be used for processing the new frame(step 614).

The method 600 may further comprise verifying whether a headphonerendering mode is used and whether an explicit DRC profile is applicableto a headphone rendering mode (step 612). In addition, the method 600may comprise verify whether an explicit DRC profile is an updatedprofile compared to a previously used profile (step 613). For thispurpose, the ID of the explicit DRC profile may be compared with the IDof a currently used profile. By doing this, it can be ensured that thedecoder 100 always uses the most current DRC profile.

Using method 600, it may be ensured that the decoder 100 alwaysidentifies a DRC profile for rendering a frame of an encoded audiosignal 102, even if the decoder 100 has not yet received the DRC profilefor the current rendering mode (i.e. for the current rendering device).Furthermore, it is ensured that the DRC profile for the currentrendering mode is applied as soon as the decoder 100 receives thecorresponding DRC profile.

As such, a method 600 for decoding an encoded audio signal 102 isdescribed. The encoded audio signal 102 comprises a sequence of frames.Furthermore, the encoded audio signal 102 is indicative of a pluralityof different dynamic range control (DRC) profiles for a correspondingplurality of different rendering modes. Examples for different renderingmodes (or different reproduction environments) are a first DRC profilefor use in a home theatre rendering mode; a second DRC profile for usein a flat panel rendering mode; a third DRC profile for use in aportable device loudspeaker rendering mode; and/or a fourth DRC profilefor use in a headphone rendering mode. A DRC profile defines a specificDRC behavior. The DRC behavior may be described by means of acompression curve (and time constants) and/or by DRC gains. DRC gainsmay be temporal equidistant gains that may be applied the encoded audiosignal 102 to deploy DRC. Compression curves may be accompanied by timeconstants which together configure a DRC algorithm. DRC typicallyreduces the volume of loud sounds and amplifies quiet sounds, therebycompressing the audio signal's dynamic range for an improved experiencein non-ideal reproduction environments.

A sequence of frames typically comprises a plurality of succeedingframes which form an audio signal. An audio program (e.g. a broadcastedTV or radio program) may comprise a plurality of audio signal which areconcatenated at splicing points. By way of example, a main audio programmay be interrupted in a repeated manner by commercial breaks. Thesequence of frames may correspond to the complete audio program.Alternatively, the sequence of frames may correspond to one of theplurality of audio signals which form the complete audio program.

Different subsets of DRC profiles from the plurality of DRC profiles maybe comprised within different frames of the sequence of frames, suchthat two or more frames of the sequence of frames jointly comprise theplurality of DRC profiles. As indicated above, the distribution of DRCprofiles across a plurality of frames of the sequence of frames leads toa reduction of a bitstream overhead for signaling the plurality of DRCprofiles.

The method 600 may comprise determining a first rendering mode from theplurality of different rendering modes. In particular, it may bedetermined which rendering mode is used for rendering the encoded audiosignal 102. Furthermore, the method 600 may comprise determining 609,610 one or more DRC profiles from the plurality of DRC profiles whichare comprised within a current frame of the sequence of frames. In otherwords, one or more DRC profiles from a subset of DRC profiles that iscomprised within the current frame may be determined. In addition, itmay be determined 611 whether at least one of the one or more DRCprofiles is applicable to the first rendering mode. The determining 611whether at least one of the one or more DRC profiles is applicable tothe first rendering mode may comprise determining a first outputreference level for the first rendering mode, determining a range ofoutput reference levels that a DRC profile from the one or more DRCprofiles is applicable to, and determining whether the first outputreference level falls within the range of output reference levels.

The method 600 may further comprise selecting 604 a default DRC profileas a current DRC profile, if none of the one or more DRC profiles isapplicable to the first rendering mode. Definition data of the defaultDRC profile is typically known at the decoder 100 for decoding theencoded audio signal 102. In addition, the method 600 may comprisedecoding (and/or rendering) the current frame using the current DRCprofile. As such, it may be ensured that a decoder 100 makes use of aDRC profile (and a dynamic range compression curve) even if the decoder100 has not yet received a DRC profile which is specific to the encodedaudio signal 102.

Alternatively or in addition, the method 600 may comprise selecting 604a first DRC profile from the one or more DRC profiles as the current DRCprofile, if the first DRC profile is determined to be applicable to thefirst rendering mode. As a result of this, the decoder 100 is configuredto use the optimal first DRC profile for the encoded audio signal 102and for the first rendering mode, as soon as the decoder 100 receivesthe first DRC profile.

The method 600 may further comprise determining 603, 606 whether thecurrent frame of the sequence of frames comprises one or more DRCprofiles from the plurality of DRC profiles, i.e. whether the currentframe comprises a subset of DRC profiles. As outlined in the context ofFIG. 5 , subsets of DRC profiles are typically comprised within I-framesof the sequence of frames. As such, determining 603, 606 whether thecurrent frame comprises one or more DRC profiles from the plurality ofDRC profiles or whether the current frame comprises a subset of DRCprofiles may comprise determining 603 whether the current frame is anI-frame. As indicated above, an I-frame may be a frame that isindependently decodable from any other frames from the sequence offrames. This may be due to the fact that the data comprised in such anI-frame is transmitted in a way that it is not depending on data fromprevious or subsequent frames. In particular, the data comprised withinan I-frame is not differentially encoded with respect to data comprisedwithin a previous or subsequent frame.

Furthermore, determining 603, 606 whether the current frame comprisesone or more DRC profiles from the plurality of DRC profiles or whetherthe current frame comprises a subset of DRC profiles may compriseverifying 606 a DRC profile flag comprised within the current frame. ADRC profile flag within the bitstream of the encoded audio signalprovides a bandwidth and computational efficient means for identifyingframes which carry DRC profiles.

The method 600 may further comprise determining whether the currentframe is indicative of an implicit DRC profile from a plurality ofimplicit DRC profiles. An implicit DRC profile may comprise apre-defined legacy compression curve and time constants that may be usedfor transcoding to E-AC-3. As indicated above, definition data of animplicit DRC profile may be known at the decoder 100 for decoding theinput audio signal 102. In contrast to the default DRC profile, theimplicit DRC profiles may be specific to different types of audiosignals (as specified e.g. in Table 1). A current frame of the sequenceof frames may indicate a particular implicit DRC profile (e.g. using anidentifier, ID). This may provide a bandwidth efficient means forsignaling an appropriate DRC profile for the encoded audio signal 102.The implicit DRC profile may be selected 608 as the current DRC profile,if it is determined that the current frame is indicative of an implicitDRC profile.

Decoding of the current frame may comprise leveling the sequence offrames to the first output reference level of the first rendering mode.Furthermore, decoding of the current frame may comprise adapting aloudness level of the current frame using the dynamic range compressioncurve which is specified within the current DRC profile. The adaption ofthe loudness level may be performed as outlined in the context of FIG. 1.

Depending on the number of frames from the sequence of frames, thecurrent DRC profile may correspond to a default DRC profile (which istypically independent of the input audio signal 102), to an implicit DRCprofile (which may be adapted to the input audio signal 102 in a limitedmanner) or to the first explicit DRC profile (which may have beendesigned for the input audio signal 102 and/or for the first renderingmode).

Typically, only a subset of frames comprises DRC profiles. Once acurrent DRC profile has been selected, the current DRC profile may bemaintained for decoding frames of the sequence of frames which do notcomprise any DRC profiles. Furthermore, the current DRC profile may bemaintained, even upon reception of frames with DRC profiles, as long asno DRC profile is received which is more up-to-date than the current DRCprofile and/or which is of higher relevance for the encoded audio signal102 (wherein the selected first explicit DRC profile has a higherrelevance than a selected implicit DRC profile which has a higherrelevance than the default DRC profile). By doing this, continuity andoptimality of the used DRC profile can be ensured.

In complement to the method 600 for decoding an encoded audio signal102, a method for generating or encoding an encoded audio signal 102 isdescribed. The encoded audio signal 102 comprises a sequence of frames.Furthermore, the encoded audio signal 102 is indicative of a pluralityof different dynamic range control (DRC) profiles for a correspondingplurality of different rendering modes. The method may compriseinserting different subsets of DRC profiles from the plurality of DRCprofiles into different frames of the sequence of frames, such that twoor more frames of the sequence of frames jointly comprise the pluralityof DRC profiles. In other words, subsets of DRC profiles, with less thanthe total number of DRC profiles, may be provided along with differentframes of the sequence of frames. By doing this, the overhead of theencoded audio signal 102 may be reduced, while at the same timeproviding the complete set of DRC profiles to a corresponding decoder100. In other words, an advantage of this approach is that an encoder150 has an increased freedom in how to transmit DRC data. This freedomcan be used to reduce the bitrate.

The sequence of frames may comprise a subsequence of I-frames (e.g.every X^(th) frame of the sequence of frames may be an I-frame). Thedifferent subsets of DRC profiles may be inserted into different (e.g.succeeding) I-frames of the subsequence of I-frames. In order to furtherreduce the bandwidth I-frames may be skipped, i.e. some of the I-framesmay not comprise any DRC profile data.

A (e.g. each) subset of DRC profiles may comprise only a single DRCprofile. In particular, the plurality of DRC profiles may comprise N DRCprofiles, with N being an integer, N>1. The N DRC profiles may beinserted into N different frames from the sequence of frames. By doingthis, the bitrate which is required for the transmission of the DRCprofiles may be minimized.

The method may further comprise inserting all of the plurality of DRCprofiles into a first frame of the sequence of frames (e.g. into thefirst frame of the sequence of frames of the audio signal). As a resultof this, the rending of the encoded audio signal 102 may be starteddirectly with the correct explicit DRC profile. As indicated above, anaudio program may be subdivided into a plurality of sub audio programs,e.g. a main audio program which is interrupted by commercial breaks. Itmay be beneficial to insert all of the plurality of DRC profiles intothe first frame of each sub-audio program. In other words, it may bebeneficial to insert all of the plurality of DRC profiles directlysubsequent to the one or more splicing points of an audio program whichcomprises a plurality of sub audio programs.

The different subsets of DRC profiles from the plurality of DRC profilesmay be inserted into different frames of the sequence of frames, suchthat each subsequence of M directly succeeding frames from the sequenceof frames jointly comprises the plurality of DRC profiles, wherein M isan integer, with M>1. In other words, the plurality of DRC profiles maybe transmitted repeatedly within blocks of M frames. As a result ofthis, a decoder 100 has to wait at the most M frames prior to obtainingan optimal explicit DRC profile for the encoded audio signal 102.

The method may further comprise inserting a flag into a frame of thesequence of frames, wherein the flag is indicative of whether the framecomprises a DRC profile or not. Providing such a flag enables thecorresponding decoder 100 to efficiently identify a frame whichcomprises DRC profile data.

The DRC profiles of the plurality of DRC profiles may be explicit DRCprofiles which comprise (i.e. which carry) definition data for defininga dynamic range compression curve. As outlined in the present document,a dynamic range compression curve provides a mapping between an inputloudness and an output loudness and/or a gain to be applied to the audiosignal. In particular, the definition data may comprise one or more of:a boost gain for boosting the input loudness; a boost gain rangeindicating a range for the input loudness, to which the boost gain isapplicable; a null band range indicating a range for the input loudness,to which a gain of 0 dB is applicable; a cut gain for attenuating theinput loudness; a cut gain range indicating a range for the inputloudness, to which the cut gain is applicable; a boost gain ratioindicating a transition between a null gain and the boost gain; and/or acut gain ratio indicating a transition between the null gain and the cutgain.

The method may further comprise inserting an indication (e.g. anidentifier, ID) of an implicit DRC profile, wherein definition data ofan implicit DRC profile is typically known to a decoder 100 of theencoded audio signal 102. The indication of an implicit DRC profile mayprovide a bandwidth efficient means for signaling a DRC profile which isadapted (in a limited manner) to the encoded audio signal 102.

As outlined above, a frame of the sequence of frames typically comprisesaudio data and metadata. A subset of DRC profiles is typically insertedas metadata.

A DRC profile may comprise definition data for defining a range ofoutput reference levels for which the DRC profile is applicable. Theoutput reference level is typically indicative of a dynamic range of arendering mode. In particular, the dynamic range of the rendering modemay decrease with increasing output reference level, and vice versa.Furthermore, a maximum boost gain and a maximum cut gain of a dynamicrange compression curve of a DRC profile may increase with increasingoutput reference level, and vice versa. As such, the output referencelevel provides an efficient means for selecting an appropriate DRCprofile (with an appropriate dynamic range compression curve) for aparticular rendering mode.

The method may further comprise generating a bitstream which comprisesthe encoded audio signal 102. The bitstream may be an AC4 bitstream,i.e. the bitstream may be compliant with an AC4 bitstream format.

The method may further comprise inserting explicit DRC gains for theencoded audio signal 102 into a frame of the sequence of frames. Inparticular, a DRC gain which is applicable to a particular frame of thesequence of frames may be inserted into the particular frame. As such,each frame of the sequence of frames may comprise a DRC data componentwhich comprises one or more explicit DRC gains to be applied to therespective frame. In particular, each frame may comprise differentexplicit DRC gains for different rendering modes. For this purpose, DRCalgorithms for different rendering modes may be applied within anencoder 150, and different DRC gains for the different rendering modesmay be determined at the encoder 150. The different DRC gains may thenbe inserted explicitly within the sequence of frames. As a result ofthis, the corresponding decoder 100 can apply the explicit DRC gainsdirectly, without performing the DRC algorithm using a dynamic rangecompression curve.

Hence, a sequence of frames may comprise or may be indicative of aplurality of explicit DRC profiles for signaling dynamic rangecompression curves for a plurality of corresponding rendering modes. Theplurality of DRC profiles may be inserted into some (not all) of theframes (e.g. the I-frames) of the sequence of frames. Furthermore, thesequence of frames may comprise or may be indicative of one or more DRCprofiles for a corresponding one or more rendering modes, wherein theone or more DRC profiles indicate that explicit DRC gains for one ormore rendering modes are inserted into the frames of the sequence offrames. By way of example, the one or more DRC profiles for signalingexplicit DRC gains may comprise a flag that indicates whether explicitDRC gains are comprised in the frames of the sequence of frames. The DRCgains may be inserted into each frame of the sequence of frames. Inparticular, each frame may comprise the one or more DRC gains which areto be used for decoding the frame.

The method may comprise inserting a DRC profile for the explicit DRCgains into a subset of frames from the sequence of frames. By way ofexample, the DRC profile for which DRC gains are transmitted may beindicative of DRC configuration data for the explicit gains.Specifically, the DRC profile for which DRC gains are transmitted may beincluded in all said subsets of DRC profiles. The DRC configuration data(e.g. a flag) may indicate that the sequence of frames comprisesexplicit DRC gains for a particular rendering mode. By doing this, thedecoder 100 is informed about the fact that for the particular renderingmode, the explicit DRC gains are to be derived directly from the framesof the sequence of frames.

Hence, the method may further comprise determining explicit DRC gainsfor the encoded audio signal 102 for a particular rendering mode. Inaddition, the method may comprise inserting the explicit DRC gains intothe frames of the sequence of frames. An explicit DRC gain may beinserted into the frame from the sequence of frames for which theexplicit DRC gain is applicable. Furthermore, a frame from the sequenceof frames may comprise the one or more explicit DRC gains which arerequired for decoding the frame within the particular rendering mode.

The method may further comprise inserting a DRC profile indicative ofDRC configuration data for the particular rendering mode into a subsetof frames from the sequence of frames (e.g. into the I-frames). The DRCconfiguration data (comprising e.g. a flag) may be indicative of thefact that for the particular rendering mode, explicit DRC gains arecomprised within the frames of the sequence of frames. As such, thedecoder 100 may determine efficiently whether to use compression curvesfrom a plurality of DRC profiles for signaling dynamic range compressioncurves or whether to use explicit DRC gains.

The DRC profiles for signaling dynamic range compression curves and theone or more DRC profiles which point to explicit DRC gains may becomprised within a dedicated syntax element (referred to e.g. as a DRCprofile syntax element) of an I-frame of the sequence of frames.

The methods and systems described in the present document may beimplemented as software, firmware and/or hardware. Certain componentsmay e.g. be implemented as software running on a digital signalprocessor or microprocessor. Other components may e.g. be implemented ashardware and or as application specific integrated circuits. The signalsencountered in the described methods and systems may be stored on mediasuch as random access memory or optical storage media. They may betransferred via networks, such as radio networks, satellite networks,wireless networks or wireline networks, e.g. the Internet. Typicaldevices making use of the methods and systems described in the presentdocument are portable electronic devices or other consumer equipmentwhich are used to store and/or render audio signals.

The invention claimed is:
 1. A method for decoding an encoded audiosignal; wherein the encoded audio signal comprises a sequence of framescomprising encoded audio data and metadata, the metadata including aplurality of different sets of dynamic range control, referred to asDRC, gains, wherein the encoded audio signal further comprises anindication of a loudness of the audio signal, and DRC configurationmetadata in one or more frames of the sequence of frames, wherein theDRC configuration metadata indicates a plurality of DRC profilesassociated with the encoded audio signal, and, for each DRC profile, arange of output reference levels for which the DRC profile isapplicable, wherein each set of DRC gains corresponds to one of theplurality of DRC profiles, the method comprising: setting a desiredoutput reference level for the decoded audio signal; identifying one ormore of the DRC profiles for which the applicable range of outputreference levels includes the desired output reference level for thedecoded audio signal; selecting one of the identified DRC profiles;decoding the encoded audio signal; adjusting the dynamic range of thedecoded audio signal by applying the DRC gains corresponding to theselected DRC profile to the decoded audio signal; determining a loudnessrelated gain in response to the indication of the loudness of the audiosignal and the desired output reference level for the decoded audiosignal; and applying the loudness related gain to the adjusted decodedaudio signal to obtain a loudness adjusted decoded audio signal havingthe desired output reference level; wherein one or more of the DRCprofiles are applicable for playback on devices with limited dynamicrange.
 2. The method of claim 1, wherein selecting one of the identifiedDRC profiles comprises selecting one of the DRC profiles applicable forplayback on devices with limited dynamic range.
 3. A decoder fordecoding an encoded audio signal; wherein the encoded audio signalcomprises a sequence of frames comprising encoded audio data andmetadata, the metadata including a plurality of different sets ofdynamic range control, referred to as DRC, gains, wherein the encodedaudio signal further comprises an indication of a loudness of the audiosignal, and DRC configuration metadata in one or more frames of thesequence of frames, wherein the DRC configuration metadata indicates aplurality of DRC profiles associated with the encoded audio signal, and,for each DRC profile, a range of output references levels for which theDRC profile is applicable, wherein each set of DRC gains corresponds toone of the plurality of DRC profiles; wherein the decoder comprises oneor more processors that: set a desired output reference level for thedecoded audio signal; identify one or more of the DRC profiles for whichthe applicable range of output reference levels includes the desiredoutput reference level for the decoded audio signal; select one of theidentified DRC profiles; decode the encoded audio signal; adjust thedynamic range of the decoded audio signal by applying the DRC gainscorresponding to the selected DRC profile to the decoded audio signal;determining a loudness related gain in response to the indication of theloudness of the audio signal and the desired output reference level forthe decoded audio signal; and applying the loudness related gain to theadjusted decoded audio signal to obtain a loudness adjusted decodedaudio signal having the desired output reference level; wherein one ormore of the DRC profiles are applicable for playback on devices withlimited dynamic range.
 4. The decoder of claim 3, wherein selecting oneof the identified DRC profiles comprises selecting one of the DRCprofiles applicable for playback on devices with limited dynamic range.5. A non-transitory computer-readable storage medium comprising asequence of instructions, wherein, when executed by an audio signalprocessing device, the sequence of instructions causes the audio signalprocessing device to perform the method of claim 1.